Aged rhesus macaques are defined as animals 19 years of age or older. The aged rhesus macaque model is increasing in importance for studies related to physiological and behavioral changes associated with aging in humans. Baseline data on the behavioral repertoire and physiology of aged rhesus macaques would serve as a valuable reference for many of these studies. Personal activity monitors, (PAM's) have been placed on six aged animals in their home cage to establish baseline levels of activity. Blood samples from twenty-seven aged animals have been collected to evaluate changes in hematological and serum chemistry values associated with aging. Currently these data are being compared across three age groups, 6-14 years, 19-24 years and 25+ years to reassess the age criteria for the definition of aged rhesus macaques.